Letters backing phoney researcher (7)

I believe the answer is:

postdoc

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'researcher' is the definition.
(someone doing postdoctoral research)

'letters backing phoney' is the wordplay.
'letters' becomes 'post' (letters in the mail or post).
'backing phoney' becomes 'doc' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'post'+'doc'='POSTDOC'

Can you help me to learn more?

(Other definitions for postdoc that I've seen before include "Researcher" , "Someone doing advanced research" .)

I've seen this clue in The Times.

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